This invention relates to a support for photographic paper being excellent in whiteness and having a sufficient adhesive strength which can be generated even through a high processing speed and a low extrusion resin temperature, and its production.
Extrusion laminating (also called extrusion coating) is widely used for the production of a support for photographic paper, wherein thermoplastic resin, such as polyolefin is melted and extruded onto the base, such as paper, in a shape of film, followed by pressing by passing a nip roller or the like to obtain the resin-coated support. In order to ensure the adhesion of resin to the base, it is necessary that the temperature of the molten resin is more than 280xc2x0 C. The base is usually treated with the surface treatment, such as the corona treatment or the flame treatment.
Under such a high temperature, resin tends to deteriorate, and gels (oxidized deteriorated resin) and streaks generate frequently. Accordingly, it was desired to lower the resin temperature upon laminating. Besides, it is necessary to raise processing speed in economical viewpoint, and it was desired to process at a high speed of 100 m/min or more.
However, lowering of the molten resin temperature and speed up of the processing speed results in the degradation of adhesive strength of resin to the base. Moreover, the base used for a support for photographic paper is essentially excellent in whiteness and flatness, and as a result, the base is inferior in adhesiveness due to its small surface roughness and inferior anchoring effect.
Accordingly, it is necessary to take a means for improving the adhesiveness. As such a means, there are the treatment of the molten resin layer with ozone, the surface treatment of the base, blending of adhesive resin to the molten resin, multilayer laminating provided with an adhesive resin layer arranged on the base side, applying anchoring agent to the base, and the like. However, adhesive resin is expensive, and anchoring agent also increases the cost caused by the great load on drying, etc.
Moreover, various means for improving the adhesive strength of resin to the base upon extrusion coating of the base with the resin were developed, such as the ozone treatment disclosed in Japanese Patent KOKOKU 61-42254 and Japanese Patent KOKAI 3-263035, the anchor coating disclosed in Japanese Patent KOKOKU 62-60970, a combination of the ozone treatment, the corona treatment and the flame treatment disclosed in Japanese Patent KOKAI 8-190171, etc.
However, by the above conventional methods, it is difficult to ensure sufficient adhesiveness, and nevertheless, the manufacturing cost is increased. Accordingly, it was still desired to develop a means capable of ensuring sufficient adhesiveness inexpensively, even employing a lower resin temperature and a high speed processing.
An object of the invention is to provide a support for photographic paper being excellent in whiteness and flatness and inexpensive, and having a sufficient adhesive strength of resin which can be generated even at a low resin temperature of 200 to 280xc2x0 C. through a high speed processing of 100 m/min or more, and a method of producing it.
The inventors investigated eagerly in order to achieve the above object, and found that the adhesiveness is improved by using a base being excellent in whiteness and flatness and incorporating unsaturated bonds into polyolefin resin.
The present invention has been completed by the finding, and provides a support for photographic paper which comprises a base having a whiteness of 75% or more and a flatness Ra of 20 xcexcm or less, and a polyolefin resin composition membrane comprising a polyolefin resin and unsaturated bond at a rate of 0.2 or more unsaturated bonds per 1,000 carbon atoms.
The unsaturated bonds may be bonded to an end of polymer chain of the polyolefin or in a compound.
Moreover, they further found that the adhesiveness is remarkably improved by surface treating of the resin surface by ozone gas or the base surface by an activating treatment, such as the corona treatment or the flame treatment.
In other words, by incorporating unsaturated bonds, the effect of the surface treatment, such as the ozone treatment, of the molten resin film is increased, and the low temperature high speed processing at 200 to 280xc2x0 C. at 100 m/min or more can be achieved in combination with the surface treatment of molten resin film and the base.